This ruined fortress, site of John the Baptist's execution, stands on an
isolated ridge 3500 feet above the Dead
Sea.

In form Machaerus resembles most of the Herodian fortresses: a cone clipped at the top. In fact, all except Herodium (which wasn't meant chiefly as a fortress) were established by the Hasmoneans. According to Josephus, it was the Hasmonean Alexander Jannaeus who first fortified Machaerus around 90 BC. The same Jannaeus conquered Transjordan (Peraea). If the desert fortresses already existed, this conquest relegated most of them to a secondary line of defense, well behind the eastern border of the expanded realm. The strongholds continued to serve, as we shall hear, on occasions when an enemy broke through. In addition, some provided safe places for treasure, arms depots and sites to execute people like the Baptist out of the public eye. Machaerus alone remained on the frontier, facing the Nabataeans to the south.

Josephus' history shows the ways in which Machaerus functioned. Upon Jannaeus' death, his widow Alexandra reigned. Having two sons by him, she appointed the elder, Hyrcanus, as high priest. The younger, Aristobulus, attracted followers. After nine years of rule the mother grew ill. Aristobulus took advantage of her condition to seize the forts where her money was, including Machaerus.

Following their mother's death, Hyrcanus and Aristobulus struggled for the kingship. Pompey the Great had just entered Syria to protect Rome's eastern frontier against the Parthians. Hyrcanus went to Damascus to seek his backing. Aristobulus set out in the same direction, but his pride overcame him: he would not bow and scrape before Rome! Instead, he withdrew to the fortress of Alexandrion (aka Sartaba; see map above). Favoring Hyrcanus, Pompey marched against Aristobulus, who withdrew further to Jerusalem. On seeing the Roman display of force, he had second thoughts and went out to surrender. Yet his own troops refused to accept the deal, and Pompey, taking Aristobulus captive, set about conquering the city (erecting siege ramps on Sabbath, when the Jews would not fight back!). It was on this occasion that Pompey stepped into the Holy of Holies, where only the high priest was permitted, traumatizing the Jews.

Pompey now held Aristobulus and his family, but a son, Alexander, managed to slip away and raise a new army. He fortified three strongholds: Alexandrion, Hyrcania and Machaerus. Then, as in the case of his father, the sheer spectacle of Roman might persuaded him to give them up. His mother, anxious for her husband and her other children, ensured that the fortresses passed peacefully into the hands of Gabinius, Pompey's man, who destroyed them.

Aristobulus was not yet finished:

Yet did Aristobulus afford another foundation for new disturbances. He fled away from Rome, and got together again many of the Jews that were desirous of a change, such as had borne an affection to him of old; and when he had taken Alexandrium [Alexandrion] in the first place, he attempted to build a wall about it; but as soon as Gabinius had sent an army against him … he was aware of it, and retreated … and marched together to Macherus; and when the king had lodged the first night upon its ruins, he was in hopes of raising another army, if the war would but cease a while; accordingly, he fortified that strong hold, though it was done after a poor manner. But the Romans falling upon him, he resisted, even beyond his abilities, for two days, and then was taken, and brought a prisoner to Gabinius, with Antigonus his son, who had fled away together with him from Rome; and from Gabinius he was carried to Rome again. Wherefore the senate put him under confinement, but returned his children back to Judea, because Gabinius informed them by letters that he had promised Aristobulus's mother [rather, wife!] to do so, for her delivering the fortresses up to him (Josephus, War I, 172-187, Whiston transl.).

This was not quite the end for Aristobulus. Julius Caesar released him from prison and took him as an ally against Pompey, but the latter's agents poisoned him before he could accomplish much.

Under Herod and Herod Antipas

It took another decade or so until Herod, with Roman backing, defeated Aristobulus' son Antigonus and secured the Jewish throne (37 BC). He rebuilt the desert fortresses that Pompey had destroyed, including Machaerus. Here is Josephus (War VII 176, Whiston translation):

When Herod came to be king, he thought the place [Machaerus] to be worthy of the utmost regard, and of being built upon in the firmest manner, and this especially because it lay so near to Arabia; for it is seated in a convenient place on that account, and hath a prospect toward that country; he therefore surrounded a large space of ground with walls and towers, and built a city there—

The city is on the eastern slope and has been only slightly excavated.

—out of which city there was a way that led up to the very citadel itself on the top of the mountain; nay, more than this, he built a wall round that top of the hill, and erected towers at the corners, of a hundred and sixty cubits high [corrected in Williamson's translation to 90 feet]; in the middle of which place he built a palace, after a magnificent manner, wherein were large and beautiful edifices. He also made a great many reservoirs for the reception of water…. moreover, he put a large quantity of darts and other machines of war into it, and contrived to get every thing thither that might any way contribute to its inhabitants' security, under the longest siege possible.

Ehud Netzer, an archaeologist who devoted much of his life to Herod's work, writes that in the case of Machaerus, Herod departed little from the Hasmonean outlines, incorporating the earlier walls in his buildings. A rectangular plan is divided into two wings, between which passed a corridor about nine feet wide (see aerial photo below). The east wing was built around a courtyard. On one side of this was a bathhouse with mosaic floors, on the other five storage rooms. In the west wing are the remains of another courtyard, larger than the first, which was surrounded by colonnades. Beside this are two halls, triclinia perhaps, which had columns that, in Netzer's view, supported a second story. Here, perhaps, lived the king and his family when visiting Machaerus.

After Herod’s death, the fortress passed to his son Herod Antipas, tetrarch of Peraea and Galilee. Antipas had ensured peace with the Nabataeans by marrying one, a daughter of King Aretas IV (a builder of Petra). Things were fine for twenty years, until, on a trip to Rome, Antipas lodged with a half-brother named Herod Philip (not to be confused with the tetrarch of that name), and became enamored of the man's wife, Herodias (Antipas' niece, in fact). Despite the inconvenience of an existing husband, Antipas proposed marriage. Herodias accepted on condition that he banish the Nabataean. The latter got word of this arrangement and moved to Machaerus, whence she slipped away to her father. Aretas, incensed, awaited a chance for revenge. It came in 36 AD. He gathered an army. Antipas did the same. The two clashed and Aretas won, although Antipas survived.

When Herodias married Antipas, her first husband was alive, according to Josephus (Antiquities XVIII 5, 4). In that case, we may assume she divorced him. By Jewish law, however, a woman could not initiate divorce, although she could do so by Roman law. (Herodias was Jewish and Roman.) If the first husband was dead, however, this still would not have legitimized the marriage. It is forbidden under Jewish law to marry one's brother's widow, unless there have been no offspring. Herodias and her first husband did have offspring—a daughter named Salome (Josephus, Antiquities XVIII 5, 4).

According to Mark and Luke, John the Baptist denounced Antipas for marrying his brother's wife. Mark 6: 17-20—

For Herod himself had sent out and arrested John, and bound him in prison for the sake of Herodias, his brother Philip’s wife, for he had married her. For John said to Herod, “It is not lawful for you to have your brother’s wife.” Herodias set herself against him, and desired to kill him, but she couldn’t, for Herod feared John, knowing that he was a righteous and holy man, and kept him safe. When he heard him, he was greatly puzzled, but he heard him gladly.

A more detailed source is Josephus. Indeed, it is thanks to Josephus' passage on the Baptist (Antiquities XVIII 5, 2, Whiston transl.) that the Church preserved his writings (there is also a short passage on Jesus, but it is of doubtful authenticity):

Now some of the Jews thought that the destruction of Herod's army [by Aretas] came from God, and that very justly, as a punishment of what he did [seven years earlier] against John, that was called the Baptist: for Herod slew him, who was a good man, and commanded the Jews to exercise virtue, both as to righteousness towards one another, and piety towards God, and so to come to baptism; for that the washing would be acceptable to him, if they made use of it, not in order to the putting away of some sins, but for the purification of the body; supposing still that the soul was thoroughly purified beforehand by righteousness. Now when others came in crowds about him, for they were very greatly moved by hearing his words, Herod [Antipas], who feared lest the great influence John had over the people might put it into his power and inclination to raise a rebellion, (for they seemed ready to do any thing he should advise,) thought it best, by putting him to death, to prevent any mischief he might cause, and not bring himself into difficulties, by sparing a man who might make him repent of it when it would be too late. Accordingly he was sent a prisoner, out of Herod's suspicious temper, to Macherus, the castle I before mentioned, and was there put to death.

Josephus omits to say that the Baptist criticized Antipas for his marriage to Herodias. Rather, he implies that the tetrarch felt threatened by John's broader message: the end-time is near and history will soon be reversed. This message could easily take a militant turn, as in fact it did less than four decades after John's death. For more on this "apocalyptic eschatology," see here and here.

In the Gospels no mention is made of Machaerus. The incidents surrounding John's death appear to be set in Galilee, not Peraea. Mark 6: 21-29 --

Then a convenient day came, that Herod on his birthday made a supper for his nobles, the high officers, and the chief men of Galilee. When the daughter of Herodias herself came in and danced, she pleased Herod and those sitting with him. The king said to the young lady, “Ask me whatever you want, and I will give it to you.” He swore to her, “Whatever you shall ask of me, I will give you, up to half of my kingdom.”
She went out, and said to her mother, “What shall I ask?”
She said, “The head of John the Baptizer.”
She came in immediately with haste to the king, and asked, “I want you to give me right now the head of John the Baptizer on a platter.”
The king was exceedingly sorry, but for the sake of his oaths, and of his dinner guests, he didn’t wish to refuse her. Immediately the king sent out a soldier of his guard, and commanded to bring John’s head, and he went and beheaded him in the prison, and brought his head on a platter, and gave it to the young lady; and the young lady gave it to her mother.
When his disciples heard this, they came and took up his corpse, and laid it in a tomb.

The ever lucid F.F. Bruce, to whom we are indebted for much in this section, suggests that the birthday party took place in Galilee (else wouldn't the gentry of Peraea have been there?) but the execution at Machaerus. The head would have been transported from the southern end of the realm to the north: "The impression we get that John’s head was delivered to the girl on a plate while the guests were still present is due to the vividness with which Mark’s tale is told." Bruce also points out that Salome would have been in her late teens and probably married already, whereas Mark, in identifying the dancer, uses the term for a young girl. The anonymous dancing daughter was likely a scion of Herodias' marriage to Antipas.

Machaerus in the Jewish revolt against Rome

Herod Agrippa, full brother to Herodias, grandson of Herod the Great and nephew to Antipas, had been brought up in Rome. One day, a servant informed on him to the emperor, Tiberius, saying he had voiced a wish that his friend Caligula should rule instead. Tiberius threw Agrippa into prison. A short time later, though, Tiberius died, and Caligula became emperor. He freed his boyhood friend Agrippas and made him King of Judaea. This aroused envy in the heart of Herodias, who commenced to nag her husband that he, who had served Rome loyally as tetrarch for over 40 years, should ask that his title be amended likewise to that of king. Antipas thought it best to leave the matter alone, but Herodias was obsessed. At last he gave in (39 AD) and went to Caligula, unaware that Agrippa had sent his old friend a letter alleging that Antipas was plotting with the Parthians and had accumulated weapons for 70,000 men. Unable to disprove the accusation, Antipas was banished to Gaul (where Herodias gracefully joined him) and his realm was added to that of Agrippas. Upon Agrippas' death in the theater at Caesarea Maritima, however, a new emperor, Claudius, reverted to the system of sending a procurator from Rome. As governor of Judaea, Galilee and Peraea, the procurator now had Machaerus.

The Jewish disappointment over Agrippas' death (he was Jewish, after all), followed by the return of the procurators, no doubt spurred some Jews into thinking that the "birthpangs" had reached their height. At the beginning of the Jewish revolt in 66 AD, says Josephus (VII 176-202) "the mass of Jews at Machaerus" so outnumbered the Roman garrison there that it surrendered. The Jews were still holding the fortress, as well as Masada and Herodium, when the Temple fell in Jerusalem (70 AD). Those who could opt for freedom fled to these three strongholds.

In 72, Lucilius Bassus, the new Roman legate of Judaea, first took Herodium and then besieged Machaerus.

It was highly necessary that this citadel should be demolished, lest it might be a means of drawing away many into a [new] rebellion, by reason of its strength; for the nature of the place was very capable of affording the surest hopes of safety to those that possessed it (Josephus, War, Whiston translation, VII 176).

Bassus set about building a siege ramp on the eastern side, the remains of which can be seen today. The Jewish rebels retreated to the upper citadel, leaving the "strangers that were with them" in the lower town. (It is not clear who these "strangers" were. Williamson translates "Gentiles," but in that case we cannot explain why the Romans later attacked them.) From the upper fort the rebels made sorties against the Romans who were building the ramp. Among the Jews was a brave, energetic youth named Elazar, who was always the first to attack and the last to return. On one occasion, however, he lingered alone outside the walls, and a daring Egyptian named Rufus stole up, lunged forward, grabbed the lad and carried him to the Roman lines. Bassus proceeded to flog Elazar in the sight of the Jews in the fortress. They were overcome with grief. Hearing their moans, and surprised at the depth of their feeling for this young man, Bassus had an inspiration. He set up a cross. The prospect of this cruelest of deaths caused even greater outcry among the rebels, and, to Bassus' delight, they offered to surrender, provided he would let them go and take Elazar with them. Bassus agreed. Apparently he wanted the fortress, not the people.

The "strangers" in the town below got word of this separate agreement and decided to escape in the night. As soon as they opened the gates, however, the Jews above sent word of the plan to Bassus. Josephus speculates (VII 202): Perhaps they were worried that Bassus would hold them responsible for the escape and annul the agreement. In the event, the Romans pursued the "strangers," killed many men, and enslaved the women and children. As for those in the fortress above, we are told that Bassus kept his agreement.

Such was the end of Machaerus. Never again did it arise as a fortress. There is no sign of later habitation on the cone-like hill, although the ruins of a Byzantine church may be seen in the nearby village of Mukawir, which preserves the basic sounds of the ancient name.